This invention relates to a process wherein a catalyst, a cocatalyst, a solvent, a monomer, a comonomer and hydrogen are added to a reactor to make polyethylene. In particular, it relates to that process where the catalyst and cocatalyst are kept separate until they are added to the reactor.
In a high pressure solution process for preparing polyethylene, the catalyst and cocatalyst are typically premixed in a small solvent stream (S1) outside of the reactor. This mixture (S1) and the main reactor feed stream (S2), which contains the remaining solvent, the monomer, and other reaction ingredients, are then separately added to a continuously stirred reactor. However, under certain production conditions of the reactor, it was difficult to control the temperature within the reactor. Specifically, the temperature within the reactor would fluctuate about 20.degree. C. every three or four minutes. This cyclical change in temperature affected the physical properties of the resulting polyethylene resin. This change in physical properties caused a swing in the extruder nose pressure, which is a direct measurement of the polymer melt flow properties through the die plate. Because of the temperature swing, the amount of monomer being reacted varied also. This was directly reflected in the amount of unreacted monomer recycled back to the reactor. No one knew what was causing this problem or how this problem could be solved.
In addition, the catalyst and cocatalyst mix tees, where the catalyst and cocatalyst were mixed with solvent in S1, would periodically plug up with solids. A plant shutdown was required several times a year to clean them. This pluggage was caused by activated catalyst solids precipitating out onto the walls of the piping system.